This invention related to multi-line telephone communications systems having one or more telephone units of which each provides access to several telephone lines and visibly indicates the status of each such line.
Multiple-line key telephones, sometimes referred to as "trader turrets", are widely used in rapid communications networks such as trading operations in banks, brokerage houses and other financial institutions. Telephones of this type provide direct access to several outside lines with the simple depression of a single key on the telephone. Dialing is unnecessary. Each telephone unit, also referred to as a telephone station, may be capable of selecting any of one-hundred, or even two-hundred, different lines, and should at the same time provide all normal telephone functions, i.e., dialing, ringing, hold, etc. One essential requirement is that each telephone station furnish an indication of the present status of each of the lines accessible at the particular station. This indication usually takes the form of a continuously lighted key for a "busy" line, a flashing key for a line on "hold" or for a "ring" on an incoming call, and a non-lighted key for a free line. In addition, the station should have the capability of indicating which line the user has picked up.
In older telephone equipment, indications of lines in use was achieved by the use of locking pushbuttons. Although all key-selecting buttons on the telephone might be lighted, the depressed key position let the user know the line he was using. The use of non-locking pushbutton keys, on the other hand, requires another type of visual indication, e.g., a lighted key or indicator. An earlier turret system using non-locking pushbuttons is described in U.S. patent Re. No. 31,144 for "Multi-Station Telephone Switching System", assigned to the assignee of the present invention.
Conventionally, all telephone systems, including those using non-locking pushbutton keys for line selection, have provided line status indication by sending a lamp excitation signal over a separate conductor for each indicator lamp. Large multiple-conductor buses carry the lamp excitation signals to each telephone station. Thus, a 200-line telephone station would require that no less than 200 conductors be connected to it merely to furnish the line status indication. In order to light the same key at each telephone station, each station must be coupled to its own 200-conductor bus. This requirement for huge numbers of status-indicating conductors in multi-station telephone systems, such as those adapted for large brokerage trading rooms, made installation and maintenance of the system difficult. Moreover, valuable space was needed upon and within the telephone console, as well as in the "equipment room" where the telephone switching equipment is located.
In addition to the huge number of lamp leads found in conventional systems, other special function conductors are generally required. These conductors, called A-leads and "Ring-not" leads, are used for hold and ringing functions In a conventional 200-line turret, where 3 conductors (an A-lead, a lamp indicating lead and a ring-not lead) were associated with each line, some 600 individual conductors might be needed, not counting the two voice leads. It can be appreciated that with such a large number of conductors to be routed, space, installation and maintenance pose increasing challenges and difficulty.
It is highly desirable to provide flexibility in the assignment of lines to individual telephone stations, i.e., to provide the opportunity for changing the lines assigned to particular keys of the telephone. In many conventional telephone systems, it is possible to change the line assignment, but only by physically changing or reconnecting wires at the switch crosspoints, or at the telephone station. This approach is cumbersome and reduces the ease with which the system may be installed and serviced.
In the telephone communications system described herein the assignment of lines to particular keys of a telephone station is completely flexible, this being achieved by storing the assignments in a programmable non-volatile electronic memory. Whenever a line assignment is to be changed from one key to a different key, it is necessary only to enter the change by reprogramming the memory. Reprogramming can be done through a personal computer terminal interfacing with the telephone equipment.
A high degree of reliability is another requirement of multi-line key telephone systems. As noted above, in multi-line "trader turrets", immediate access to an outside line can be extremely critical A system-wide breakdown obviously would be disasterous, since it would cut off all communication between the traders and the outside world. Therefore, a high degree of reliability of the overall system is required. This means reliability both in establishing connections between the telephone station and a given outside line, and in ensuring against a larger-scale breakdown in the event of electronic or mechanical component failure.
The present invention is adaptable to distributive logic, which minimizes the effect of unusual or unexpected equipment and component failures. This is achieved by making all incoming lines available to every telephone station. An internal failure at a particular telephone station does not interfere with the other stations. Similarly, telephone data processing may be handled in several individual "cards", each of which controls only a limited number of (e.g., four) lines or telephone stations. Thus, a failure in a "line card", due to electrical overloading, for example, affects at most four lines. In the event of failure, all stations have access to all remaining outside lines. A failure in a "master card" would cause four telephone units to be unusable, but all lines would remain operative from the remaining station. In either case the malfunction is corrected by simply replacing the failed card.